This invention relates to phthalocyanine photoconductive materials and, more particularly, to a novel process for the preparation of X-form metal phthalocyanine.
It is known that images may be formed and developed on the surface of certain photoconductive materials by electrostatic means. The basis xerographic process, as taught by Carlson in U.S. Pat. No. 2,297,691, involves uniformly charging a photoconductive insulating layer and then exposing the layer to a light-and-shadow image which dissipates charge on the portions of the layer which are exposed to light. The electrostatic image formed on the layer corresponds to the configuration of the light-and-shadow image. This image is rendered visible by depositing on the imaged layer a finely divided developing material comprising a colorant called a toner and a toner carrier. The powder developing carrier will normally be attracted to those portions of the layer which retain a charge, thereby forming a powder image corresponding to the latent electrostatic image. This powder image may then be transferred to paper and other receiving surfaces. The paper then will bear the powder image which may subsequently be made permanent by heating or other suitable fixing means. The above general process is also described in U.S. Pat. Nos. 2,357,809; 2,891,011, and 3,079,342.
Phthalocyanine, which also is known as tetrabenzotetraazaporphin and tetrabenzoporphyrazine, may be said to be the condensation product of four isoindole groups. Metal-free phthalocyanine has the following general structure: ##STR1## In addition to the metal-free phthalocyanine of the above structure, various metal derivatives of phthalocyanine are known in which the two hydrogen atoms in the center of the molecule are replaced by metals from any group of the periodic table. Also, it is well known that from one to sixteen of the peripheral hydrogen atoms in the four benzene rings of the phthalocyanine molecule may be replaced by halogen atoms and by numerous organic and inorganic groups. The following discussion is directed primarily to substituted and unsubstituted metal phthalocyanines.
Metal phthalocyanines are known to exist in at least three well known polymorphic forms, namely, the alpha, beta and gamma forms. These forms may be easily distinguished by comparison of their X-ray diffraction patterns and/or infrared spectra. There is some question whether the reported gamma form is actually a separate polymorph, or is instead merely a less crystalline form of alpha phthalocyanine. In addition to these three well known forms, which exist in both metal-containing and metal-free phthalocyanine, additional polymorphs of metal-containing phthalocyanine are known, i.e., R-form disclosed in U.S. Pat. No. 3,051,721, "delta" form described in U.S. Pat. No. 3,160,635 and another "delta" form described in U.S. Pat. No. 3,150,150.
In U.S. Pat. No. 3,357,989, it is disclosed that an especially sensitive form of meta-free phthalocyanine, known as "X metal-free" phthalocyanine, could be prepared by extended dry milling or grinding of the alpha or beta form metal-free phthalocyanine. In copending application Ser. No. 566,839, abandoned for continuation Ser. No. 10,077 now U.S. Pat. No. 3,594,163, a second method for the preparation of "X metal-free" phthalocyanine is disclosed and claimed. This method comprises mixing the alpha crystalline form of metal-free phthalocyanine with a portion of the X metal-free form and an aliphatic organic solvent, and maintaining the mixture until the alpha metal-free form is converted to the X metal-free form. Both of these methods are very time consuming and expensive.
The known methods of preparing metal-phthalocyanines include the reaction of phthalonitrile with a metal or metal salt in quinoline and trichlorobenzene; the reaction of phthalic anhydride, phthalic acid, or phthalamide, urea metal salts, and a catalyst; the reaction of o-cyanobenzamide with a metal; and the reaction of phthalocyanine or replaceable metal phthalocyanine with a metal forming a more stable phthalocyanine. The metal phthalocyanines prepared by the above methods are generally in the alpha or beta polymorphic forms.
Metal phthalocyanines are widely used in the preparation of inks and paints. However, one important drawback of using many of the known metal phthalocyanines in this mode is that they recrystallize in the presence of heat and strong solvents. Electrophotographic plates comprising metal phthalocyanines in a binder are disclosed in copending application Ser. No. 518,450, filed Jan. 3, 1966, now U.S. Pat. No. 3,816,118. One distinct disadvantage of employing said metal phthalocyanines in this mode is that they show low photosensitivities as compared to metal-free phthalocyanines. Thus, there is a continuing need for metal-phthalocyanines with greater electrical photosensitivities and greater stability to recrystallization in the presence of heat and strong solvents.
Copending application Ser. No. 756,365 now abandoned, filed in the U.S. Patent Office on Aug. 30, 1968, discloses and claims metal phthalocyanines in the X polymorphic form as well as a method for their preparation. More specifically, this method comprises rapidly sublimating a metal phthalocyanine polymorph under a pressure of about 10.sup.-.sup.1 to about 10.sup.-.sup.6 Torr. This method, while quite fast and while producing a high yield of substantially pure X-form metal phthalocyanine, requires the use of complex and expensive evaporation equipment, especially when it is desired to industrially prepare X-form metal phthalocyanine on a large scale.
Since large quantities of X-form metal phthalocyanine may be needed for electrophotographic, pigment, and/or other uses, there is a continuing need for a simpler, cheaper, less time consuming, and more reproducible method of preparing same.
It is, therefore, an object of this invention to provide a method of preparing X-form metal phthalocyanine and phthalocyanine compounds devoid of the above-noted disadvantages.
Another object of this invention is to provide a direct method for the preparation of X-form metal phthalocyanine and phthalocyanine compounds.
Still another object of this invention is to provide a more rapid method of preparing X-form metal phthalocyanine than previously known methods.
Yet another object of this invention is to provide a method of preparing substantially pure X-form phthalocyanine and phthalocyanine cmpounds wherein the yield of the resulting product is very high.
A further object of this invention is to provide a reliable and dependable method of preparing X-form metal phthalocyanine and phthalocyanine compounds which gives highly reproducible results.
Still another further object of this invention is to provide a method of preparing X-form metal phthalocyanine and phthalocyanine compounds which requires inexpensive heating and cooling techniques.
It is another object of this invention to provide an economical method of preparing X-form metal phthalocyanine and phthalocyanine compounds when it is to be produced on a large scale industrial level.